The present invention relates to video boards for use in, for example, personal computers, and more particularly to video boards supporting both a 1-bit plane video board mode for a black/white monitor and a 2-bit plane video board mode for a 4-gray level monitor.
Heretofore, a known monochrome video board has supported a 2-gray level (black and white) monochrome monitor. Recently, however, an improved monochrome video board has been developed to support a 4-gray level(black, white, gray1 and gray2) monochrome monitor for graphics.
The former 2-gray level monochrome monitor usually must use the 1-bit plane board for supplying two kinds of video intensity (black and white) and the latter 4-gray level monochrome monitor must use the 2-bit plane video board for supplying four kinds of video intensity (black, white, gray1 and gray2). Conventionally, the two video boards have different hardware. That is, since the 2-gray level monochrome monitor and the 4-gray level monochrome monitor each utilizes its own bit plane operation, they have not been compatible with each other. Therefore, the 1-bit plane video board can never support the 4-gray level monitor, and if the 2-bit plane video board is connected to the black/white monitor, it may have considerable disadvantages not only in memory allocation and race problems but also in cost.